It is clear everyone is starting to get it. Word of mouth or referrals bring in business because it brings credibility. Tom Fishburne's cartoon aptly shows the power of word of mouth over other advertising.
NPR had a segment this morning about something called Buzz Agents. Marketing agencies, realizing the power of word of mouth, are signing up people to use products and then talk up how great they are. These "buzz agents" do it for free use of the product.
Business owners are sitting on a gold mine of happy customers. Their own personal buzz agents. Those happy customers could be even more effective if they were given opportunities to share and even something of value to give to their friends.